Method for producing a heat exchange and heat exchanger

ABSTRACT

A method for producing a heat exchanger may include: a) applying an adhesive layer to an outer side of heat exchanger tubes by laminating at least one of an adhesive sheet and an adhesive film; b) expanding the tubes on a longitudinal end side in a connecting region via an expanding mandrel; c) arranging the tubes parallel to one another such that the tubes lie flat against one another via the connecting region; and d) heating the adhesive layer at least in the connecting region of the tubes to adhesively bond the tubes to one another via the connecting region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No.PCT/EP2016/068667 filed on Aug. 4, 2016, and to German Application No.DE 10 2015 215 045.3 filed on Aug. 6, 2015, the contents of each ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method for producing a heat exchangercomprising tubes. The invention furthermore relates to such a heatexchanger.

BACKGROUND

For decades now, cooling modules have been manufactured for use ofrefrigerant and use of coolant, the cooling modules generally beingmanufactured with materials which are suitable for brazing, for examplestainless steel, copper or aluminum. Said materials as semifinishedproducts are coated with brazing metal. The braze plating of thesemifinished products consists of a material layer which has a lowermelting point than the basic material. For the brazing, the parts arebraced and are subsequently brazed in the furnace at a temperature whichreaches close to the melting point of the basic material. Among itemsneeded for this purpose are, for example, fluxing agents which breakopen or dissolve the oxide layer located on the outside. However,fluxing agents have the disadvantage of being harmful to health; inaddition, residues can remain on the components, the residues having anegative effect on the required purity of the component. In addition,the brazing can usefully only connect materials of the same type to oneanother in order, for example, to absorb thermal elongations or not toallow the latter to arise at all. Similarly, from a corrosion aspect,there should not be any differences in potential between components ofvarying materials. The brazing can proceed successfully only if variousboundary conditions, as follows, are observed: degreasing the parts,stacking and bracing the braze-plated semifinished products by means ofbrazing frames, brazing in the furnace at around 650° C. for severalhours, checking the tightness of the parts and optionally re-brazing theparts should they not be tight.

This process is highly time-consuming, costly and resource-intensive,which has a negative effect on the CO2 balance. During the connection oftwo joining partners composed of different materials, different thermalexpansions have to be taken into consideration and compensated for,which can ensure brazing only to a limited extent or has only a certaincreep strength.

Such heat exchangers are therefore disadvantageous in that theproduction thereof is highly costly and resource-intensive and damagingto the environment. Furthermore, only a limited number of materials aresuitable for brazing, wherein the components have to be produced frommaterials of the same type or similar materials in order to achievereliable brazing. In addition, components composed of differentmaterials cannot be connected to one another at the required quality, ifat all.

The present invention is therefore concerned with the problem ofspecifying, for a method for producing a heat exchanger and for such aheat exchanger, an improved or at least a different embodiment which isdistinguished in particular by more economical production.

This problem is solved according to the invention by the subject matterof the independent claims. Advantageous embodiments are the subjectmatter of the dependent claims.

SUMMARY

The present invention is based on the general concept of, in the case ofa heat exchanger according to the invention comprising tubes, for thefirst time deforming and expanding a longitudinal end region of suchtubes by means of an expanding mandrel in such a manner that toconnection of the individual tubes is possible exclusively via theexpanded, in particular plane, connecting regions, and therefore, inthis case, a tube plate which up to now has been used in this region canbe entirely dispensed with. This makes it possible not only to reducethe diversity of parts, but in addition also to reduce the manufacturingcosts. The heat exchanger according to the invention is produced by anadhesive layer first of all being applied to an outer side of theindividual tubes by lamination of an adhesive sheet or an adhesive film.The lamination of the adhesive layer onto the outer side of the tubesconstitutes a particularly economical manufacturing process which alsomakes it possible to apply a particularly thin, but nevertheless uniformadhesive layer. The tubes are subsequently expanded on the longitudinalend sides in the respective connecting region by means of an expandingmandrel, thus resulting in flat connecting regions via which theindividual tubes can later lie against one another and can be adhesivelybonded to one another. The tubes are then arranged parallel to oneanother such that they lie against one another via their respectiveconnecting regions and at the same time form channels between theindividual tubes and outside the connecting regions, through whichchannels a fluid can flow perpendicularly to the tubes. In order then tobe able to connect the individual tubes to one another, the adhesivelayer is heated at least in the connecting regions, whereupon theindividual tubes are fixed to one another via their respectiveconnecting regions. By means of the expanded connecting regions, theindividual tubes are already held at a distance from one another, andtherefore a tube plate which has been used up to now in the longitudinalend region of the tubes can now be completely omitted. In addition, bymeans of the use of an adhesive layer for connecting the individualtubes, a brazing connection which has been used up to now in this regioncan be dispensed with, as a result of which, in turn, considerableadvantages can be realized. For example, different materials, inparticular materials with different coefficients of thermal expansion,can now also be easily connected to one another without there needing tobe concern about stresses or cracks in the region of the connection.Furthermore, the adhesive layer constitutes an electrical isolator whichprevents galvanic corrosion (contact corrosion) in metals of differentpotentials. In addition, removal of fluxing agent residues can also beomitted, as can a complicated preparation of the brazing points, forexample by degreasing.

The heating of the adhesive layer preferably leads to a change in shapeand/or change in structure of the adhesive layer, which permits and/orfacilitates connection of the tubes. Such a change to the adhesive layeris, for example, softening and/or melting and/or expansion and/orhardening of the adhesive layer. The connection between the componentsby means of the adhesive layer preferably achieves a stable state afterthe adhesive layer cools following the heating. This is the case inparticular whenever the adhesive layer cures.

The connection of the tubes by means of thermal adhesive bondingfurthermore has the advantage that they can be separated from oneanother when required simply and/or without residues of the adhesivelayer. This advantageously takes place by the fact that the adhesivelayer is heated again, wherein the adhesive layer is heated in such amanner that the adhesive layer can be separated from at least one of thecomponents. It is thereby in particular possible to dismantle the heatexchanger after expiry of its service life into its individual partssimply and neatly and also according to type and to thereby betterrecycle said heat exchanger.

The adhesive layer has at least one adhesive means which, for curing,requires a temperature of between 80° C. and 400° C. in order to connectthe associated connecting regions. Examples of such adhesive means areMakrofol®, Bayfol®, Kleberit 701.1-701.9 and the like. The adhesivelayer advantageously has an adhesive which has thermoplastic properties.That is to say that the adhesive can be deformed above anadhesive-specific temperature which preferably corresponds to thetemperature during heating of the adhesive layer in order to connect thecomponents.

The method according to the invention for connecting the tubesfurthermore makes it possible to heat the adhesive layer for arelatively short time. The duration of the heating is advantageouslyselected here in such a manner that a sufficient connection is achieved.In particular, it is possible by means of the method according to theinvention to heat the adhesive layer for fewer than 10 minutes. Such ashort duration of heating the adhesive layer leads to reducedconsumption of energy, and therefore the heat exchanger can be producedin a cost-effective and environmentally friendly manner. Such a shortheating duration is achieved in particular by an appropriate choice ofthe adhesive layer and/or of the layer thickness of the adhesive layer.

Use is preferably made of adhesive layers which have a relatively smalllayer thickness. The method according to the invention permits adhesivelayers with a layer thickness of 5 μm or less to be used. In particular,use is made of adhesive layers with a layer thickness of between 5 μmand 500 μm.

In order to improve the connection between the tubes and/or in order toachieve a desired relative positioning of the tubes relative to eachother, the tubes are pressed against each other via their connectingregions with a contact pressure. It is also conceivable to press thetubes against one another during and/or after heating.

The contact pressure here can be arbitrarily large or small. The limitsof the contact pressure are provided here firstly by the fact that thecontact pressure is intended to lead to an improved connection of thetubes, and, secondly, undesirable damage to same is not intended to becaused. The method is preferably configured in such a manner here thatcontact pressures of between 0.1 N/mm² and 0.7 N/mm² are used for thispurpose.

In preferred variants, the contact pressure is produced by the expandingmandrels which are already used for expanding the longitudinal endregions and which are pushed into the respective tubes, wherein thecontact pressure is realized by expansion of the tube. Refinements inwhich the expanding mandrel is additionally used for heating theadhesive layer are particularly preferred. That is to say that theexpanding mandrel can be heated, and therefore upon or during thepushing of the expanding mandrel into the associated tube, the adhesivelayer is heated and the contact pressure realized at the same time. As aresult, the connection of the tubes is realized in just a few methodsteps and as simply and effectively as possible, in particular within areduced time.

The adhesive layer can also be heated in any other manner. For example,it is possible to heat the adhesive layer in an furnace. The heating ofthe adhesive layer in an furnace makes it possible in particular tocarry out other method steps for producing the heat exchanger in thefurnace.

In order to improve the adhesive connection and/or in order to shortenthe time required for producing the adhesive connection, the adhesivelayer can be cooled after heating. This cooling can be realized in anymanner. For example, cooling can be achieved by the fact that theheating of the adhesive layer is time-limited. The cooling can also takeplace actively by the components being guided or arranged in anenvironment having a reduced temperature.

Specific cooling of the adhesive layer can also take place by the factthat a cooling device is brought into contact with the components or theadhesive layer.

In an advantageous development of the solution according to theinvention, a fin structure, for example corrugated fins, is introducedbetween two adjacent tubes and is adhesively bonded to said tubes viathe adhesive layer arranged in each case on the outside of the tubes.This makes it possible to achieve a particularly good transfer of heatinto the flow channel formed by two adjacent tubes in each case.

Expediently, at least part of a collector is arranged in the region ofthe connecting regions, said part comprising the connecting regionswhich are each arranged on the same side, and said part lying with anedge against the adhesive layer of a connecting region of a tube andbeing adhesively bonded to the latter. In this case, it is thereforepossible not only to connect, that is to say to adhesively bond, theindividual tubes to one another via their respective connecting regions,but additionally also to adhesively bond a collector, for example awater box or at least part of same, thereto. By this means, theproduction of the heat exchanger according to the invention isconsiderably further simplified, as a result of which the economicalefficiency thereof can be increased in turn.

The advantages of the heat exchanger according to the invention and ofthe production method thereof reside in a simpler and morecost-effective design. By means of this method, as known in general inadhesive bonding, a wide variety of materials having differentcoefficients of thermal expansion and corrosion potential can beconnected to one another, with at the same time extremely thin layerthicknesses. For the electronic cooling, for example, the processing ofcopper material as a functional surface for the brazing or sintering ofelectronic components is required time and again. However, thisprocessing is not possible with current brazing furnaces sinceimpurities due to the processed copper lead to corrosion to the aluminumcomponents. On account of the thin thicknesses of the adhesive layer,high thermal conductivity is ensured, which is of great advantage inparticular in stacked-plate coolers. In addition, the required hightightness, which is generally produced only in the case of welded orbrazed components, is also ensured. By means of the small thickness ofthe adhesive layer, in particular in the form of an adhesive sheet, theadhesive bond is substantially more cost-effective than, for example,epoxy or silicone adhesive. Application of the adhesive in bead formwould require a much higher amount of material than is necessary. Thistherefore saves material, resources and therefore ultimately costs.Furthermore, the processing of the adhesive is considerably simplifiedsince the processing of the adhesive does not require any machines(pump, nozzle, valve), merely the pressing together of the parts.Furthermore, savings are produced by means of a more rapid and simplerprocessing of the parts; in particular, curing times in the furnace, ofseveral hours, for the crosslinking are not required. The laminatedadhesive layer requires only approx. 3 minutes under a correspondingheated device for the adhesive bonding of the individual parts, saiddevice applying the pressure for the time mentioned.

Further important features and advantages of the invention emerge fromthe dependent claims, from the drawings and from the associateddescription of the figures with reference to the drawings.

It goes without saying that the features mentioned above and those whichhave yet to be explained below are usable not only in the respectivelystated combination but also in other combinations or on their ownwithout departing from the scope of the present invention.

Preferred exemplary embodiments of the invention are illustrated in thedrawings and are explained in more detail in the description below,wherein the same reference numbers refer to identical or similar orfunctionally identical components.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in each case schematically:

FIG. 1 shows a sectional illustration through a heat exchanger accordingto the invention with expanding mandrels for expanding longitudinalend-side connecting regions of individual tubes,

FIG. 2 shows an illustration as in FIG. 1, but without expandingmandrels and with part of a collector.

DETAILED DESCRIPTION

According to FIG. 1, a heat exchanger 1 according to the invention hastubes 2, the longitudinal end regions 3 of which open according to FIG.2 into a collector 4, for example a water box, of which only part isillustrated. The tubes 2 are expanded here at the longitudinal endregion 3 and are thereby provided with a connecting region 5 via whichthey lie against one another and thereby form or bound channels 6 whichrun in the orthogonal direction with respect to the tubes 2, arearranged between the tubes 2 and run perpendicularly to the plane of theimage according to FIGS. 1 and 2. According to the invention, theindividual tubes 2 are adhesively bonded to one another via theirlongitudinal-end-side connecting regions 5, and therefore a tube platewhich has customarily been provided up to now in this region can becompletely omitted, as a result of which not only can the diversity ofparts be reduced, but in addition so too can the weight and theproduction costs of the heat exchanger 1 according to the invention.

The heat exchanger 1 according to the invention is produced here asfollows: first of all, in a method step a), an adhesive layer 7 isapplied to an outer side of the individual tubes 2 by lamination of anadhesive sheet 8 or an adhesive film 9. Such a lamination of theadhesive layer 7 can not only take place here economically, but alsoextremely precisely and with an extremely small layer thickness.Subsequently, the tubes 2 in method step b) are expanded on thelongitudinal end sides in their respective connecting region 5 by meansof an expanding mandrel 10, specifically in such a manner that theconnecting regions 5 of two adjacent tubes 2 lie flat against each othervia the adhesive layer 7 arranged in between. The tubes 2 in method stepc) are now arranged parallel to one another such that they lie againstone another via their respective connecting regions 5. Subsequently, inmethod step d), the adhesive layer 7 is heated at least in theconnecting regions 5 for the adhesive bonding of the tubes 2 and, as aresult, the individual tubes 2 are fixed with respect to one another.

The adhesive layer 7 can be heated here, for example, to a temperatureof between 80° C. and 400° C., wherein the warming or heating has to beapplied only for a short time, for example less than 10 min, inparticular 2 to 3 min. During the adhesive bonding, the connectingregions 5 can be pressed against one another with a contact pressure ofbetween 0.1 N/mm² and 0.7 N/mm², for example by means of the individualexpanding mandrels, as a result of which a more stable adhesive bond canbe achieved. Customarily, however, the pressure in terms of themanufacturing is not applied by the expanding mandrels 10, but ratheronto the stack from above and then the latter is brought to atemperature (cf. FIG. 2). Furthermore, the expanding mandrels 10 canhave a heating device and can be heated as a result, and therefore theexpanding mandrels 10, after applying the contact pressure, can also beused at the same time for local heating of the adhesive layer 7.Alternatively, of course, the adhesive layer 7 can also be heated in afurnace. In order to be able to reduce a cycle time for producing theheat exchanger according to the invention, provision can also be made tocool the adhesive layer 7 after the heating, that is to say after methodstep d).

The adhesive layer 7 is preferably applied here with a layer thicknessof between 5 μm and 500 μm, that is to say partly with a very smalllayer thickness which, however, permits electrical insulation and areliable connection and a certain elasticity between the componentsadhesively bonded to one another. The electrical insulation isparticularly of great advantage here if, for example, tubes 2 and/orother components of different materials, that is to say with differentelectrical potentials, are intended to be connected to one another.

For example, a fin structure 11, in particular in the manner ofcorrugated fins, can be introduced in the channels 6, that is to saybetween the individual tubes 2, said fin structure likewise being fixedto the opposite outer sides of two adjacent tubes 2 via the adhesivelayer 7. The fin structure 11 can be introduced here before the tubes 2are adhesively bonded to one another or after same.

Looking once again at FIG. 2, it is possible to see that at least partof the collector 4 is arranged in the region of the connecting regions5, said part comprising the connecting regions 5 and lying with an edge12 against the adhesive layer 7 of a connecting region 5 of an outertube 2 and being adhesively bonded to the latter. The collector 4 isonly partially illustrated here according to FIG. 2.

With the production method according to the invention and the heatexchanger 1 according to the invention, the latter can therefore beproduced simply and more cost-effectively, with it being possible at thesame time to connect a wide variety of materials having differentcoefficients of thermal expansion and corrosion potential to oneanother, with at the same time a minimum use of adhesive. In addition,the lamination of the adhesive layer 7 onto an application of such anadhesive in bead form, which is associated with a significantlyincreased requirement of material, can be dispensed with. This alsosimplifies the processing of the adhesive considerably since, forexample, no pumps, nozzles or valves which have to be cleaned in acomplicated manner retrospectively are required. By means of thecomparatively rapid curing time of the adhesive layer 7 according to theinvention, the cycle time for the production of the heat exchanger 1according to the invention can also be reduced, which likewise has anadvantageous effect on the production costs. In comparison to brazingconnections which have been used up to now in this region, the adhesivelayer 7 which is used is also significantly more cost-effective than,for example, expensive brazing metal and, in addition, a complicatedremoval of fluxing agent residues is omitted. The significantly reducedamount of energy which is required can also be considered to be afurther advantage of the adhesive connections. It is above all alsopossible to use materials which cannot be brazed but which can betightly connected to one another by means of the adhesive connectionaccording to the invention.

1. A method for producing a heat exchanger comprising: a) applying anadhesive layer to an outer side of heat exchanger tubes by laminating atleast one of an adhesive sheet and an adhesive film; b) expanding thetubes on a longitudinal end side in a connecting region via an expandingmandrel; c) arranging the tubes parallel to one another such that thetubes lie flat against one another via the connecting regions; and d)heating the adhesive layer at least in the connecting region of thetubes to adhesively bond the tubes to one another via the connectingregions.
 2. The method as claimed in claim 1, wherein the adhesive layeris heated in step d) to a temperature of between 80° C. and 400° C. 3.The method as claimed in claim 1, wherein the adhesive layer is heatedin step d) for a duration of less than 10 minutes.
 4. The method asclaimed in claim 1, wherein heating the adhesive layer includes pressingthe connecting region of the tubes against one another with a contactpressure of between 0.1 N//mm² and 0.7 N/mm² to form an adhesivelybonded connection.
 5. The method as claimed in claim 4, wherein heatingthe adhesive layer includes heating the expanding mandrel for heatingthe adhesive layer.
 6. The method as claimed in claim 1, wherein theadhesive layer is heated in a furnace.
 7. The method as claimed in claim1, further comprising cooling the adhesive layer after step d).
 8. Themethod as claimed in claim 1, wherein applying the adhesive layerincludes forming a layer thickness of between 5 μm and 500 μm.
 9. Themethod as claimed in claim 1, further comprising inserting a finstructure between two adjacent tubes and adhesively bonding the finstructure to the two adjacent tubes via the adhesive layer.
 10. Themethod as claimed in claim 1, further comprising arranging at least partof a collector in a region of the connecting region of the tubes, the atleast part of the collector including the connecting region of the tubeseach being arranged on the same side, and adhesively bonding an edge ofthe at least part of the collector the connecting region of each tube.11. A heat exchanger comprising: a plurality of tubes having anoutwardly expanded longitudinal end structured with a flat connectingregion on an outer side thereof; an adhesive layer disposed on theconnecting region of the longitudinal end of the plurality of tubes, theadhesive layer including at least one of a laminated adhesive sheet anda laminated adhesive film; and wherein the plurality of tubes arearranged parallel to one another such that the connecting region of eachof the plurality of tubes lie flat against one another, and wherein theplurality of tubes are adhesively bonded to one another at theconnecting region view the adhesive layer.
 12. The heat exchanger asclaimed in claim 11, wherein the adhesive layer has a layer thickness ofbetween 5 μm and 500 μm.
 13. The heat exchanger as claimed in claim 11,further comprising a fin structure arranged between two adjacent tubesof the plurality of tubes.
 14. The heat exchanger as claimed in claim13, wherein the fin structure is adhesively bonded to the two adjacenttubes of the plurality of tubes via the adhesive layer.
 15. The heatexchanger as claimed in claim 11, further comprising a collectordisposed at the longitudinal end of the plurality of tubes, wherein theplurality of tubes open into the collector.
 16. The heat exchanger asclaimed in claim 15, wherein the collector is a water box.
 17. Themethod as claimed in claim 2, wherein heating the adhesive layerincludes pressing the connecting region of the tubes against one anotherwith a predefined contact pressure.
 18. The method as claimed in claim17, wherein the predefined contact pressure ranges from 0.1 N/mm² to 0.7N/mm².
 19. A method for producing a heat exchanger, comprising: a)applying an adhesive layer to an outer side of heat exchanger tubes bylaminating at least one of an adhesive sheet and an adhesive film; b)expanding the tubes on a longitudinal end side in a connecting regionvia an expanding mandrel; c) arranging the tubes parallel to one anothersuch that the tubes lie flat against one another via the connectingregion; and d) adhesively bonding the tubes to one another via theconnection region by heating the adhesive layer at least in theconnecting region of the tubes to a predefined temperature and pressingthe tubes against one another at the connecting region with a predefinedcontact pressure.
 20. The method as claimed in claim 19, wherein atleast one of: the predefined temperature is between 80° C. and 400° C.;and the predefined contact pressure is between 0.1 N/mm² and 0.7 N/mm².